Thermal timer



NOV. 17, 1942. GQMERSALL 2,302,117

THERMAL TIMER v Filed March 14, 1942 s Sheets-Sheet 1 IN V EN TOR.

/3 /0/ F K? N GOMERSALL Jf/i77 [92% A T TORNE Y Nov. 17, 19 2. J. R.GOMERSALL 2,302,117

' THERMAL TIMER Filed March 14. 1942 3 Sheets-Sheet 2 IN VEN TOR. JOHNF? GONE/PEA L 4 ATTORNEY Nov. 17, 1942. J. R. GOMERSALL THERMAL TIMERFiled March 14, 1942 3 Sheets-Sheet 3 .9 INVENTOR.

' C/OH/V R Goms RsAu ATTORNEY Patented Nov. 17, 1942 2,302,117 THERMAL'mma John R. Gomersall, Elgin, Ill., assignor to Me Graw ElectricCompany, Elgin, 111., a corporation of Delaware Application March 14,1942, Serial No. 434,752

4 Claims.

My invention relates to timing mechanisms and more particularly tothermal timers.

An object of my invention is to provide relatively simple andhighly'eifective means to ensure proper operation of a thermallyactuable element constituting a part of a thermal timer.

Another object of my invention is to provide a relatively simple meansto ensure continuity of the initial rate of change of. a thermallyactuable element with time.

Another object of my invention is to provide relatively simple meansoperatively associated with a thermal timer for causing an increase inthe energizing current flowing through a heating element adapted tocause heating and consequent flexing of the blmetal element of thethermal timer.

Other objects of my invention will either be obvious from a descriptionand the drawings comprising a part of this application or will bepointed out in the course of such description and embodying myinvention, the section being taken on the line l-i of Fig. 3 and showingthe parts in the normal or non-toasting positions,

Fig. 2 is a fragmentary vertical longitudinal sectional viewtherethrough taken on the line 2-2 of Fig. l,

Fig. 3 is a vertical longitudinal sectional view taken on the line 3--3of Fig. 1, the parts being shown in the same positions as in Fig. 1,

Fig. 4 is a fragmentary plan view looking upwardly into the toaster, toshow the positions of certain parts of the timer when the toaster is notoperating,

Fig. 5 is a fragmentary front view of a controlling means associatedwith the thermal'timer,

Fig. 6 is a fragmentary and generally diagrammatic view of the parts ofthe thermal timer in normal or non-toasting positions,

Fig. 7 is a view similar to Fig. 6 except that the parts are shown inthe positions occupied thereby just after the start of a toastingoperation,

Fig. 8 is a view similar to Fig. 7 except that the bimetal bar hasflexed to a greater degree, and,

Fig. 9 is a view similar to Fig. 8 except that fully operative toasterstructure with which is associated a thermal timer of the kind disclosedin my issued Patent No. 2,266,024, to which timer the details embodyingmy present invention have been added.

The toaster structure ii may include a moulded skeleton frame 13 of akind now used in the art and a bottom plate 1 5, which may be ofinverted dish shape, suitably secured to the upper surface of theskeleton frame 13. The toaster structure includes also a casing l1comprising front, rear and side walls open at the top and the bottom anda top or-cover member l3, all as now well known in the art. I providealso a rethe parts are shown in the positions they occupythat I considernecessary in order to disclose a movable crumb tray H which may besecured in any suitable or desired manner to the skeleton frame I3.

The toaster includes further a plurality of pairs of planarvertically-extendingelectric heating elements 23 which may each includeone or more thin sheets of electric insulating material, such as mica,having wound thereon a heating resis'tor strand or wire 25, all in amanner now well known in the art. The toaster includes also a rearintermediate wall 21 and a front intermediate wall 29, the upper andlower ends of which may be supported in any suitable or desired mannerso that they will remain in their desired and proper operative positionsduring toasting operations. The toaster includes also a bread carrier 3|located between each pair of vertical toast heating elements 23 and itis, to be understood that the toaster may be designed for toastingeither one slice of breadonly at one time or a plurality of such slices.

,. The carrier or carriers 3i may be secured to a carriage plate 33which is adapted to move vertically reciprocally from its uppernon-toasting position shown in Figs. 1 and 3 to a lower toastingposition. Means for yieldingly biasing the carriers 3i in their uppernon-toasting position may include a tension coil spring 35, the lowerend of. which is connected to a convenient part of carriage plate 33 andthe upper end of which is connected to a bracket 31, of substantially L-shape, secured to the front intermediate wall 29.

The carriage plate 33 is provided with upper and lower guide bushings orbearings adapted to move on a vertical standard 33 and the carriage'plate may be provided with a plurality of rollers ll adaptedto lightlyengage the front surface of intermediate wall 23 to prevent excessturning movement of the carriage plate on the vertical standard 39.

I provide further a secondary carriage plate 42 movable verticallyrelatively to the carriage plate 33 being held thereon by headed rivets43. Member 42 has integral therewith a forwardly projecting portion 45which is'adapted to move in a suitable slot in the front wall of outercasing i1 and has mounted thereon an actuating knob 1 whereby anoperator or user of the toaster may, by pressing downwardly on the knob,cause downward movement of the carrier and of the carriage portions IIand 42 into toasting positions.

Carriage plate 33 has pivotally mounted thereon a latch lever arm 4! thelower forwardly-bent end portion thereof being adapted to engage under ahook member 5i pivotally mounted at the upper end of a detent" which ispivotally mounted on a suitable bracket I! supported against the undersurface of bottom plate ll. Detent member 53 is generally of L-shape and'a biasing spring 51 connected with the upper portion of hook member 5!and with the bottom plate I! normally yieldingly biases the detent andthe hook member 5| into the position shown in Fig. 1 of the drawingswhich is substantially the normal or release position of these parts.

Means for reducing the upward speed of the bread carriers and thecarriage 33 may include an air cylinder 59 having movable therein apiston mounted on the upper end of a piston rod 6i which is connectedwith carriage 33 by a lostmotion means well known in the art.

The toaster is further provided with terminals 83 for the heatingelements and may have connected therewith a twin conductor cord 81.Means for controlling the energization of the heating elements 23 mayinclude contact members 68 insulatedly mounted on the bottom plate it atits forward left-hand corner and these contact members may be engaged bya contact bridging member H insulatedly supported by a resilient bar 13secured to the side portion of the carriage plate 33.

I have illustrated in the various drawings constituting a part of thisapplication, the thermal timer which is disclosed and claimed in myissued Patent No. 2,266,024 assigned to the same assignee as is thepresent application and reference may be had to this patent for thedetails of this timer and its method of operation and only suchreference to the various parts shown in the drawings in this applicationand their method of operation will be made as are considered necessary.

A lever arm 15 is pivotally supported on a pivot pin 11 which may besuitably supported as by a wall of a casing 19 in which the thermaltimer may be positioned or in any other suitable or desired manner. Bar1! has movably mounted thereon, longitudinally thereof, a latch bar 8!which may be held closely adjacent to one surface of the bar 15 as byheaded pins and be normally yieldingly biased thereto into an operativeposition by a small coil tension spring 83. The left-hand end of latchbar II is provided with an angularly projecting portion 8! adapted toengage under a laterally projecting lug 81 on detent bar 53. when latchlever 49 is moved downwardly it will engage an intermediate portion ofdetent arm 58 and cause a limited degree of turning movement thereof ina counter-clockwise direction so that lug I! may move into engagementwith the nose ll of bar 8| and then thereunder whereby the breadcarriers will be held in toasting position for a length of timedetermined by means new to be described. Y

A bimetal bar I. has one end thereof pivotally supported as by a pivotpin II and has mechanically rigidly secured thereto, at its pivoted end.a rigid bar 93, the main portion of which is spaced from the bar ll andextends parallel thereto as long as the bimetal bar I is substantiallystraight. mally yieldingly bias the bar If and the bimetal bar I! in acounter-clockwise direction with the result that the free end of thebimetal bar ll zestsfigainst a projecting portion 81 of arm or Thebimetal bar II has insulatedly mounted thereon a small heating coil 0!which is normally connected in series circuit relation with the toastheating elements 28, all as now well known in the art.

The terminals of the heating coil I! have connected therewith conductorsleading to two fixed contact terminals Ill supported by any suitablemeans which contact terminals are adapted to be engaged under certainoperating conditions by a contact bridging member I". This contactbridging member is supported at the lower end of a vertically extendingrod I", which rod is normally yieldingly biased upwardly by acompression coil spring Ill. When the carriage ll is moved downwardly, alaterally projecting portion I" thereon is moved downwardly into contactwith a washer ill on the bar llll, all as set forth in my earlierpatent. Downward movement of the contact bridging member I" and rod I0!is initially prevented by the bimetal bar "which extends in a planesubstantially at right angles to the plane of the arm 15, as is showncorrectly in Fig. 2 of the drawings, while Figs. 6, "I, 8 and 9 showthese parts apparently in the same plane but this has been done for easeof illustration.

Let it be assumed that knob 41 has been moved downwardly to eifectmovement of the carrier and a slice of bread thereon into toastingposition with the result that heating element ll on the bimetal bar isis energized which will have the result shown more particularly in Fig.7 of the drawings, namely that the bimetal bar will flex to the shapeshown in Fig. 7. The result of this will be that rigid bar 93 is turnedtoward the left and when bimetal bar I! has flexed to a predetermineddegree, this bar ll will engage against an adjustable stop bar IIIsuitably supported in the path of travel of rigid bar 03. Fig. 5 showsan adjusting means in the shape of a knob II! at the front of thetoaster which knob is adapted to move a cam disk ill to thereby adjustthe position of the end of stop bar HI relatively to the rigid bar l3.When bar 83 is prevented from further turning movement in acounterclockwise direction, the flexing bimetal bar 88 will tend to movein a clockwise direction with the result that it will no longer engagelug 81 but move slightly away therefrom into a relatively deep recessIll in bar I! (see Fig. 9) whereby bar 15 may move slightly in aclockwise direction with the result that contact bridging member I" onrod ll! may engage contact members IM whereby the heating element as isshort-circuited. This means that further heating .of the bimetal bar andits flexing as a result thereof is stopped and the bimetal bar will nowcool and flex in the opposite direction with the result that rigid barII will be given a turning movement in a clockwise direc- A coil springii tends to nortion. At a certain position of rigid bar 93 it willengage a nose or lug I2I at the right-hand end of bar 9I whereby, uponfurther cooling of the bimetal bar 99, bar 9I is moved toward the rightand out of interlocking engagement with lug 91 on thedetent member 93with the result that latch 49 on carriage 33 will be disengaged from thehook member ti and will move upwardly quickly because of the action'ofthe tension spring 35.

Toasters of this general kind are usually tested and adjusted to operateproperly at some assumed standard voltage at the factory which circuitvoltage may be 115 volts since the greater maiority of supply circuitsto which such toasters are usually connected in operation approximatethis value. It is, however, possible that a toaster of this kind may beconnected to a supply circuit the voltage of which is relatively verymuch lower, say 105 volts. or even 100 volts in th cases of circuitswhich are overloaded at certain times of the day or night. It isfurtherpossible that a toaster or this kind may be connected to circuits whichare operating at excessively high voltage such as 120 or eventl25 voltsand it has been found difllcult to so design, construct and. adjust theheating element 99 on a given bimetal bar v99 that, in combination withthe other parts of such a thermal timer, the degree of toasting desired,say medium, will be obtained at 100 volts, 115 volts and at 125 voltswithout any adjustment of knob H5.

It is, of course, necessary to provide such a length of operation of atoaster that it is possible to obtain darktoast on the relatively lowvoltage and this. of course, means that the length of such a toastingoperation is relatively long, say on the order or three minutes or more,while the length of a toasting operation to obtain light toast on a highvoltage may be on the order of a minute or even slightly less; It may behere pointed out that turning movement of adjusting member II! willcause a shift in the position of bar II9 to the right or to the left andwhen bar H3 is moved to the right, as seen in Figs. 6 to 9 inclusive,the 4 heating-up period of the heater 99 is less than it would be if thestop bar I I3 had been move toward the left.

I have found that when no additional means of control is provided on atoaster operating on the principle of first heating up a bimetal bar andthen oi permitting it to cool to a given temperature to determine thelength of a toasting operation, it is almost impossible to maintain therate of flexing of the bimetal bar at a constant value or a given lengthof time, this applying particularly to the final or last period ofenergization of the heater 99 since it is impossible in view of thehereinbefore described operating conditions to design and use a heatingcoil for the bimetal bar 99 of relatively high or.- increased wattagesince this would tend to shorten the length of toasting period obtainedby a thermal timer of this kind to too small a length of toastingoperation when dark toast is to be obtained when the toaster isenergized at say 100 volts. I

I therefore provide a plurality of auxiliary resisters I29 and I25suitably supported in the timer casing 19 and means actuated by thebimetal bar during its flexing incident to its being heated toincrease'the current in heating coil 99. For this purpose I- provide asubstantially fixed contact against a stop member I3I and-outofengagement with contact member I21. This spring contact arm I29 isconnected to one terminal of resistor I23 and the other terminals of thetwo resistors 5 are connected by suitable conductor to one terminalof'the heating element 99. I provide further a second spring contact armI33 which is normally biased into engagement with the contact member oncontact arm I29 in a manner shown 0 more particularly in Fig. 6 of thedrawings. Arm

I33 is connected to the other terminal or heating element 99 as will benoted by reference to Figs. 6 to 9 of the drawings. I

Arm I33 has mounted thereon a small lug I 35 at its free end which lugis adapted to be engaged be noted that member I3! is initially out ofengagement with insulating lug I a long as the bimetal bar 99 is at roomtemperature as will be the case when the toaster is not in operation orfor a short period of time after the start of a toasting operation.

Referring now to Fig. 7 or the drawings, it will be noted that thedegree of flexure of bimetal bar 89 is such that actuating member I3'Ihas been moved into engagement with lug I39 on arm I33 80 and that amI33 has been moved against its bias to a degree suificient to permitcontact arm I29 to move. under its own bias, out of engagement withfixed contact member I21 with the result that resister I29 is no longerconnected in shunt circuit 35 relation relatively to electric heater 99.This will have the result that the current traversing heater 99 isincreased to a desired degree.

Referring now to Fig. 8 of the drawings, it will be noted that flexureof bimetal bar 99 has increasedto such an extent that spring contact armI33 has been moved out of engagement with contact arm I29 with theresult that resistor I23 has also been disconnected from its original orinitial shunt position relatively to heater 99 so that a furtherincrease in the current traversing heater 99 is effected.

As 'has already been referred to, it is obvious that the heat radiatedfrom the heater 99 and the bimetal bar may become so great, at higher 0temperatures of the heater and of the bimetal bar, that relativelylittle if any increase in temperature of the bimetal bar can be effectedwith the result that the desired continuous flexure of the bimetal barnecessary to properly operate the timer will not be eflected. However,by increasing the current in the manner just above described, bydisconnecting shunting resistors from the circuitof the heating element99, it is possible to ensure vigorous continued flexure or the bimetalbar 00 so that it is possible to obtain the required tion of the bimetalbar 99 and the resultant turning movement of bar III to thereby causeshortcircuiting of the heater 99.

The device particularly embodying my invention and including theauxiliary resistors thus provides efllcient and relatively simple meansactuable by the bimetal bar itself through suitable means operativelyassociated therewith to obtain the desired result, namely continuedflexure of the bimetal bar at a uniform rate per unit of time even atthe higher temperatures of the timer parts involved particularly indetermining the length of time of a toasting operation.

Various modifications may be made in th structures embodying myinvention without departing from the spirit thereof and all suchmodifications clearly coming within the scope of the appended claims areto be considered as being covered thereby.

I claim as my invention:

' 1. In a thermal timer for measuring a time interval comprising abimetal bar and an electric heating element therefor adapted to beenergized to cause heating of the bimetal bar and flexing thereofin onedirection and then to be deenergized to cause cooling of the bimetal barand flexing thereof in the opposite direction, the improvementcomprising a resistor connected in electric circuit with said electricheating element and switching means actuable by said bimetal bar whenbeing heated to cause deenergization of said resistor and an increase inthe amount of current carried by the electric heating element as saidheating progresses.

2. In a thermal timer for measuring a time interval comprising a bimetalbar and an electric heating element therefor adapted to be energized tocause heating of the bimetal bar and flexing thereof in one directionand then to be deenergized to cause cooling of the bimetal bar andflexing thereof in the opposite direction, the improvement comprising aplurality of resistors, plural contact switching means, electricconnections between the electric heating element, the plurality ofresistors and the switching means and means actuable by said bimetal barwhen flexing while being heated to cause an increase in the amount ofcurrent carried by the electric heating element as said heatingprogresses.

3. In a thermal timer for measuring a time interval comprising a bimetalbar and an electric heating element therefor adapted to be energised tocause, heating of the bimetal bar and flexing thereof in one directionand then to be deenersized to cause cooling of the bimetal bar andflexing thereof in the opposite direction, the improvement comprising aplurality of resistors normally connected in shunt circuit with saidelectric heating element and switching means for said resistors actuableby said bimetal bar when being heated to cause sequential disconnectionof said resistors and an increase in the amount of electric currentcarried by saidelectric heating element as the heating of said bimetalbar prosresses.

4. In a thermal timer for measuring a time interval comprising a bimetalbar and an electric heating element therefor adapted to be energized tocause heating-of the bimetal bar and flexing thereof in one directionand then to be deenergized to cause cooling of the bimetal bar andflexing thereof in the opposite direction, the improvement comprising aresistor connected in electric circuit with said electric heatingelement and switching means actuable by said bimetal bar when beingheated to cause deenergization of said resistor and to maintain thedegree of flexing of said bimetal bar per unit of time substantiallyconstant during the heating period.

Joan a. oounnsann.

